The present invention relates to an apparatus and a process for recovering sorbic acid with effectiveness.
Sorbic acid is produced by decomposing (e.g., a decomposition using acids or alkalis, or thermal decomposition) a polyester prepared by reacting crotonaldehyde with ketene. Among such decomposition methods, acidolysis, particularly hydrolysis with hydrochloric acid is advantageous in view of yield and quality.
The production of sorbic acid utilizing a decomposition using hydrochloric acid is typically carried out by a recrystallization method comprising the steps of; reacting crotonaldehyde with ketene to prepare a polyester, heat-decomposing the polyester dispersed in hydrochloric acid, cooling and filtrating the reaction product to obtain a crude sorbic acid, dissolving the crude sorbic acid in hot water, hot-filtrating, and cooling the filtrate for crystallization, thereby producing purified sorbic acid. Since the recrystallization method involves the production of a large amount of a recrystallization mother liquor (filtrate) containing sorbic acid at a low concentration, efficient recovery of the sorbic acid from the mother liquor is difficult. Furthermore, the recrystallization mother liquor can not be discharged directly in view of environmental pollution because of the biochemical oxygen demand (BOD) of the mother liquor being high.
Japanese Patent Publication No. 13456/1986 (JP-B-61-13456) proposes a process for producing purified sorbic acid which comprises subjecting wet cakes of a crude sorbic acid prepared by acidolysis of a polyester to recrystallization, in which the pH of a dilute solution of the sorbic acid (recrystallization mother liquor) from the recrystallization step is adjusted to 5-7 and the resultant solution is concentrated by reverse osmosis, and from the resultant concentrated solution are recovered the precipitated crystals of sorbic acid. The literature mentions that the solvent extraction method is disadvantageous.
The method of the literature, however, requires an apparatus for the reverse osmosis, and a highly efficient recovery of sorbic acid with a simple apparatus and a simple operation with a consequent reduction in the BOD of the waste liquid (filtrate) cannot be expected. A technology for an effective and efficient reduction in the BOD has not been proposed yet.
Therefore, an object of the present invention is to provide an apparatus and a process for recovering sorbic acid that ensure a highly efficient recovery of sorbic acid from a waste liquid (e.g., crystallization mother liquor such as a filtrate) produced in a sorbic acid production step, such as in a recrystallization step.
Another object of the present invention is to provide an apparatus and a process for recovering sorbic acid that ensure an effective reduction in the BOD of a waste liquid and a recovery of highly pure sorbic acid from crude sorbic acid with high efficiency.
Another object of the present invention is to provide an apparatus and a process for recovering sorbic acid that enable an efficient recovery of highly pure sorbic acid from a waste liquid produced in the production of sorbic acid and also effectively reduce the BOD of the waste liquid by recycling an extracting solvent without a complicated apparatus and operation.
The inventor of the present invention did extensive investigations to attain the above objects, and found that sorbic acid can be extracted from a crystallization mother liquor with a high extractability by using a specific solvent, thereby the BOD of a waste liquid is significantly reduced. The present invention has been accomplished based on the above findings.
Accordingly, the recovering apparatus of the present invention is an apparatus for recovering sorbic acid from a waste liquid produced in a production step of sobic acid (e.g., in a recrystallization step of crude sorbic acid) by at least solvent extraction, which comprises an extraction unit for extraction of sorbic acid from the waste liquid using an organic solvent in which not less than 0.5% by weight of sorbic acid is dissolvable, separable from water, and having a solubility in water not more than 1% by weight. In this apparatus, for example, the crystalline sorbic acid formed by crystallization of crude sorbic acid may be separated from a waste liquid (a mother liquor) and the waste liquid may be subjected to the above-mentioned solvent extraction. The extract from the aforementioned solvent extraction unit may be treated with an alkali in a back (reverse) extraction unit to extract sorbic acid in the form of a salt. Moreover, the extract from the back extraction unit may be at least neutralized with an acid in a treatment unit followed by the separation of sorbic acid from the treated mixture in a separation unit. Furthermore, the organic solvent separated in the back extraction unit may be recycled to the extraction unit through a recycle line. As the extraction solvent, there may be used alcohols, ketones, hydrocarbons, esters, ethers, etc.
According to the process of the present invention, sorbic acid is recovered by extracting sorbic acid from the waste liquid (e.g., mother liquor) using the above organic solvent.